Summary: Generates an index (or "tag") file for objects found in source files.

The ctags program generate an index (or "tag") file for C, C++, Eiffel,
Fortran, and Java language objects found in files. This tag file allows
these items to be quickly and easily located by a text editor or other
utility. A "tag" signifies a language object for which an index entry is
available (or, alternatively, the index entry created for that object).
Alternatively, ctags can generate a cross reference file which lists, in
human readable form, information about the various source objects found in
a set of language files.